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Jeep Wiring - After the Fire

Posted in How To: Electrical on June 12, 2007 Comment (0)
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We've all had stuff go wrong off-road, and whether it's something as massive as a fire or something as mundane as an ignition switch, all hope isn't lost. OK, so we are talking about the 45 years of carbureted Jeeps, not you new-fangled foos-injection guys. If you had a fire or other catastrophe, odds are good you're missing some sensors you'll need to get your engine to run.

For the carbureted Jeeps, as long as the steering wheel isn't locked, it's really easy to get the Jeep to go-and often drive it all the way home after a mishap. Heck, we've even used this temporary fix for weeks (if not months) before.

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If you have swapped a higher-output alternator into your Jeep or just swapped an engine into your older Jeep, you might have experienced the wiring gremlin that lets your Jeep start just fine but doesn't let it stop. The majority of us who have had this problem are running a Delco-style 10SI or 12SI alternator with three wires going into the case on the alternator. Here's a breakdown of the wires you'll see going into or coming out of the alternator (depending on your point of view):

Batt: This is the post on the back of the alternator. It should go directly to the main power junction in your system (if so equipped) or to the battery with at least a four-gauge wire.

Terminal #1: There will be a "1" or an "R" (for relay) cast into the case. This is one of two wires going into a plug on the side of the case. This terminal was originally intended to go to ground if the alternator died. That action triggers a light in the dash that most often says "Batt." This tells you that your alternator, battery, or something else in your charging system has gone south.

Terminal #2: Again, there will be a "2" or an "F" (for field or sense) cast into the alternator case. This is one of two wires going into a plug on the side of the case. This is the exciter terminal that tells the alternator when to start charging. Most often, it just goes to the positive on the battery. It can be hooked to the "Batt" lug on the back of the alternator.

If you are experiencing the engine running after shutting off the key, your alternator is most likely receiving current on the #1 wire. The first thing to do is to make sure you haven't run the wire back to the same terminal on your key switch that the battery and voltage-gauge connection are run to. If you have, these two wires need to go to a different terminal.

The next thing that might be occurring is there is no battery light in your vehicle. If this is the case, try installing a light in series with the wire; that is, install it in line with the #1 wire. Another way to fix this is to install a diode (1A/100V) in line on this wire. Make sure the stripe on the end of the diode that indicates which direction the electricity can flow is toward the alternator.


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